Ferrous alloy



Patented Jan. 23, 1934 UNITED FERROUS ALLOY Victor 0. Homerberg, Belmont, Mass., assignor ta The Nitromal Corporation, Albany, N. Y., a corporation of Delaware No Drawing. Application May 10, 1929 Serial No. 362,135

4 Claims.

My invention relates to ferrous alloys and particularly to white, mottled and malleable cast irons containing elements rendering them amenable to surface hardening by the nitriding process.

While it has been proposed to harden ordinary castiron by subjecting it to the action of ammonia at a temperature of from 900 to 1800 degrees Fahrenheit, experimental work along this line has indicated the impossibility of obtaining a product which, from a practical or commercial viewpoint, is satisfactory.

No appreciable hardening can be attained by nitriding ordinary cast iron at a temperature as low as 900 degrees F., nor can such iron be hardenedto an appreciable degree by nitriding at temperatures as high as 1800 degrees F., without additional heat treatment. Furthermore, the case produced in either instance is brittle and susceptible to spalling and exfoliation.

It has also been proposed to harden gray cast iron alloys by the Fry nitriding process thereby obtaining a final hardness said to correspond to that of hard chilled castings or, in other words, to the hardness of white cast iron to which this invention more particularly relates.

White cast iron is, however, difficult or almost impossible to machine but can be malleableized and is adapted for many uses for which gray cast iron is Wholly unsuited. When malleableized it may be machined, and if, thereafter, the surface portions subjected to wear can be appreciably hardened, the field of application will be enormously extended.

In order to appreciably harden steel by nitriding, certain alloying elements such, for example, as aluminum, chromium, molybdenum, etc., must be incorporated therein. It is not apparent that the addition to White cast iron of such alloying elements which are essential or at least desirable to produce a satisfactory nitride hardened surface will not prevent the malleableizing of the iron. Nor is it apparent that after malleableizing such a white cast iron alloy it can be again hardened by nitriding to a degree sufiicient to make a commercially desirable product. I find, however, that by the addition to white cast iron containing the usual elements and having the usual total carbon content of say from about 2% to 4.5% of from 0.15% to 5% of aluminum, and from 0.1% to 8% of an element or combination of elements taken from the following group, to wit; boron, chromium, molybdenum, nickel, titanium, tungsten, zirconium and vanadium, an alloy is obtained which can be malleableized and thereafter nitride hardened in the malleableized state at a comparatively low temperature.

For example, a white cast iron containing- Percent Carbon ('total) more than 2.0 Aluminum 1.0-2.0 Chromium 1.5

Molybdenum 0.4 Silicon 0.90-2.83

may be successfully hardened by nitriding at a temperature not exceeding the AC1 point.

As another example, a white cast iron containing about 1.0% each of aluminum and chromium may be subjected to the regular malleableizing cycle, and an extremely hard, tough, coherent and adherent case, more than one-thirty second of an inch in thickness, produced thereon by nitriding for about forty hours at 975 degrees Fahrenheit.

In all cases, to avoid warping and distortion in treating such a cast iron by the nitriding process it is extremely important that the operation be conducted at a temperature which is not in excess of the thermal critical point (Aci point) of the alloy.

What I claim is 1. An article of manufacture composed of malleableized cast iron having. nitride hardened surface portions, and containing more than 0.15% and less than 5% of aluminum as an essential ingredient, and from 0.1% to 8% of an element selected from the groupboron, chromium, molybdenum, nickel, titanium, tungsten,

vanadium and zirconium.

2. An article of manufacture composed of malleableized cast iron having nitride hardened surface portions, and containing more than 0.15% and less than 5% of aluminum as an essential ingredient, and from 0.1% to 8% of a combination of elements selected from the groupboron, chromium, molybdenum, nickel, titanium, tungsten, vanadium and zirconium.

3. An article of manufacture composed of malleableized cast iron having nitride hardened surface portions, and containing more than 0.15% but not over 2% of aluminum as an es-- sential ingredient, and from 0.1% to 8% of an element selected from the groupboron, chromium, molybdenum, nickel, titanium, tungsten, vanadium and zirconium.

4. An article of manufacture composed of malleableized cast iron having nitride hardened surface portions, and containing more than 0.15% but not over 2% of aluminum as an essential ingredient, and from 0.1% to 8% of a combination of elements selected from the groupboron, chromium, molybdenum, nickel, titanium, tungsten, vanadium and zirconium.

VICTOR O. HOMERBERG. 

